This invention relates to improvements in a vibration reducing system for internal combustion engines mounted on automotive vehicles, which is intended for reducing vibrations of an internal combustion engine due to fluctuations in combustion pressure, and more particularly, to a vibration reducing system for internal combustion engines, which effectively reduces both roll vibration and rotational fluctuations in an internal combustion engine.
Hitherto, a vibration reducing system for internal combustion engines has been proposed in Japanese Patent Provisional Publication No. 6-33990. In this proposition, a sub-flywheel system is provided to an engine in addition to a main flywheel system including a crankshaft and a flywheel so as to be rotatingly driven in a direction opposite to the direction of rotation of the main flywheel system. A roll moment is generated by reaction forces exerted on bearing portions of these two flywheel systems. Use of this roll moment cancels roll vibration which is a vibration in a direction of rotation about a longitudinal axis of an internal combustion engine, produced by torque fluctuations generated every combustion in respective cylinders of the internal combustion engine.
With the above conventional arrangement, the condition for fully canceling roll vibration of an internal combustion engine is represented by the following formula (1):
I1=xcfx81I2xe2x80x83xe2x80x83(1)
where I1 is an inertial mass of the main flywheel system; I2 is an inertial mass of the sub-flywheel system; and xcfx81 is a speed increasing ratio of a sub-flywheel system.
A large roll vibration reducing effect can be obtained in the vicinity of such a condition. However, since the main flywheel system inherently has a large inertial mass I1, it is necessary to adequately increase the inertial mass I2 of the sub-flywheel system or ensure a large speed increasing ratio xcfx81 as apparent from the above formula (1), in order to fully cancel the inertial mass I1 of the main flywheel system. However, a large-sized sub-flywheel is necessary in order to increase the inertial mass I2 of the sub-flywheel system, which will incur an increase in weight of an entire engine. Also, when the speed increasing ratio is made large, bearing portions of the sub-flywheel system, which rotates at high speeds, will be degraded in durability. Because of these various factors, the above-mentioned device cannot fully cancel roll vibration of an internal combustion engine, and is limited in its effect.
Additionally, with the above conventional arrangement, although it is possible to reduce roll vibration of an engine, there is a problem that rotating fluctuations of an engine rotating shaft (crankshaft) cannot be reduced.
Therefore, it is an object of the present invention to provide an improved vibration reducing system for an internal combustion engine, by which drawbacks encountered in conventional vibration reducing systems can be effectively overcome.
Another object of the present invention is to provide an improved vibration reducing system for an internal combustion engine, which can effectively reduce both roll vibration and rotational fluctuations generated in the internal combustion engine.
A further object of the present invention is to provide an improved vibration reducing system for an internal combustion engine, which can effectively reduce engine vibrations while sharply reducing booming noise generated in a passenger compartment in a vehicle during idling of the engine.
An aspect of the present invention resides in a vibration reducing system for an internal combustion engine, comprising an elastic member, and a rotating member driven through the elastic member by a rotating shaft of the engine. Here, the elastic member and the rotating member are arranged such that one of frequencies obtained by multiplying a rotational frequency of the rotating shaft of the engine which is operated in a predetermined engine operating condition where an engine speed is generally constant by a value (a natural number/2) is within a range between a frequency of antiresonance for a rotational fluctuation of the rotating shaft of the engine which antiresonance is generated under a resonance generated by the elastic member and the rotating member and a frequency of antiresonance for roll vibration of the engine which antiresonance is generated under a resonance generated by the elastic member and the rotating member. It will be understood that the above range contains the frequency of antiresonance for the rotational fluctuation and the frequency of antiresonance for the roll vibration.
Another aspect of the present invention resides in a vibration reducing system for an internal combustion engine, comprising a rotational vibration system including an elastic member, and a rotating member driven through the elastic member by a rotating shaft of the engine, the rotational vibration system generating resonance having a frequency of resonance. Here, the elastic member and the rotating member are arranged to select the frequency of resonance in a manner that one of frequencies obtained by multiplying a rotational frequency of the rotating shaft of the engine which is operated in a predetermined engine operating condition where an engine speed is generally constant by a value (a natural number/2) is within a range between a frequency of antiresonance for a rotational fluctuation of the rotating shaft of the engine which antiresonance is generated under the resonance generated by the rotational vibration system and a frequency of antiresonance for roll vibration of the engine which antiresonance is generated under the resonance generated by the rotational vibration system.
A further aspect of the present invention resides in a vibration reducing system for an internal combustion engine, comprising an elastic member, and a rotating member driven through the elastic member by a rotating shaft of the engine. Here, the elastic member and the rotating member are arranged such that one of frequencies obtained by multiplying a rotational frequency of the rotating shaft of the engine which is operated in a predetermined engine operating condition where an engine speed is generally constant by a value (a natural number/2) is within a range between a frequency of antiresonance for a rotational fluctuation of the rotating shaft of the engine which antiresonance is generated under a resonance generated by the elastic member and the rotating member and a frequency of antiresonance for roll vibration of the engine which antiresonance is generated under a resonance generated by the elastic member and the rotating member. The vibration reducing system further comprises a drive rotational inertial mass member and a driven rotational inertial member corresponding to the rotating member. The drive and driven rotational inertial mass members are relatively rotatably connected through the elastic member. The drive and driven rotational inertial mass members and the elastic member constituting a rotational vibration system and forming part of a driving force transmitting mechanism through which a rotational driving force of the rotating shaft of the engine is transmittable. Here, antiresonance is generated in the rotational vibration system between vibration in the rotational vibration system and rotational vibration at a predetermined frequency range generated under operation of the engine. Additionally, a spring force of the elastic member has a non-linear characteristics relative to a relative rotational angular displacement between the drive and driven rotational inertial mass members. The spring force of the elastic member has a characteristics to increase with an increase in the relative rotational angular displacement.